It is a worrisome time in this wealthy port city, known for its 19th-century churches and busy canals, where more than 100 people have fallen ill since the outbreak of a potentially lethal form of E. coli, putting 20 patients in intensive care, including five pregnant women.
Adding to the anxiety is the failure, so far, to identify the source of the infection.
“Very mysterious,” said Dr. Jörg F. Debatin, medical director at the University Medical Center, Hamburg-Eppendorf.
Hamburg is a proud and diverse city that has found itself at the center of global crises before: It struggled to counter its reputation as a breeding ground for Islamic extremism after it was revealed that some of the men who carried out the terrorist attacks on Sept. 11, 2001, lived, studied, worshiped and plotted here.
It has inched its way back, attracting tourists and young people who regularly fill its bars and restaurants and stroll its sprawling red light district, the largest in Europe.
This time, the scare is over a health crisis that appears to have emerged in or around the city.
Since the outbreak four weeks ago, 18 people have died and 1,730 have fallen ill, including 520 who have developed the most serious complications, known as hemolytic uremic syndrome, or H.U.S.
The Robert Koch Institute, Germany’s disease control agency, said the majority of the most serious infections have been reported within a short driving distance from the city: 97 here, 143 in Schleswig-Holstein, 82 in North Rhine-Westphalia and 51 in Lower Saxony.
In the United States, health officials said that the strain of E. coli involved in the outbreak was rare but not unknown. An unusual aspect of the outbreak is that the bacteria has incubated for as long as 12 days in the intestines of those infected before they became sick. Typically, E. coli infections take three days to turn into full-blown illness. The long incubation period makes it even more difficult for investigators to track the source of the outbreak.
On Friday, as panic continued to grip the streets here and across Europe, officials cautiously said the peak of the crisis might have passed.
The “situation seems to have calmed somewhat, as far as the number of new infections is concerned,” said Dr. Reinhard Brunkhorst, the president of the German Nephrology Society.
But experts said it was too soon to say if that was the case, adding that while they believed tomatoes, cucumbers and lettuce were the source of the bacteria, they were not sure. Researchers believe that because a high number of infections spread across a single region of one country, the bacteria probably entered the food chain after leaving farms, but before the produce was sold directly to consumers, said Jonathan Fletcher, a senior lecturer in microbiology at the University of Bradford in England.
“The distribution suggests this wasn’t at the point of origin because given the way food chains work these days that means it would have already spread more widely across Europe and possibly the world,” he said. “At the same time, this has already traveled far enough to suggest that not just one stall or supermarket was responsible.”
None of this speculation, though, did anything to calm a jittery public, especially in a nation where people are generally risk averse.
“I stopped eating salads as soon as I heard about the outbreak,” said Holger Schettler, a 68-year-old sailor visiting Hamburg. “I will not eat another bit of salad until they find the causes.” His wife nodded in agreement.
Tuti Fernanco, a waiter at Vesuvio Restaurant, which is near Hamburg’s main railway station, said: “I haven’t sold a green salad for days. Customers just ask for broccoli, or chips. No more salads. None. I am really surprised by the public reaction.”
Hlakan Dogan, manager of a döner kebab takeaway stand close to the central shopping mall, said he was experiencing the same thing. “Customers are very, very cautious now,” he said. “You can no longer automatically serve a salad with the kebab.”
Not surprisingly, vegetable vendors said their businesses were suffering.
At Hamburg’s fruit, vegetable and flower market, one of Europe’s largest, there were few customers and lots of angry and bewildered merchants watching their inventories spoil. The market was built in 1962, and, until recently, annual sales were running close to $3 billion.
Torsen Berens, the market manager, said he could not say precisely how much sales had fallen.
“All I can say is that it’s bad, very bad,” he said. “Let’s hope they find the source.”